Low density and high density polyethylene films have been used as heavy-duty bags for packaging granular materials such as rice and wheat, powdery materials such as fertilizer and feed, and angular solid materials such as fowl. These films, however, suffer from various disadvantages; for example, the low density polyethylene film is necessary to be increased in thickness because of its poor mechanical strength, and the high density polyethylene film is not satisfactory in sealing properties and strength against angular products and moreover inferior in appearance.
In order to overcome the foregoing problems, a bag has been developed which is made of a laminated film comprising low density and high density polyethylene films (see Japanese Patent Application Laid-Open Nos. 30994/1980 and 92023/1981). However, the bag described in Japanese Patent Application Laid-Open No. 30994/1980 is readily subject to blocking because its inner layer is made of low density polyethylene, and has the problems that it is difficult to open and the inner surfaces of the bag can slide only with difficulty. The bag described in Japanese Patent Application Laid-Open No. 92023/1981 is inferior in a film puncture strength, tear strength, impact resistance at low temperatures, and so forth and is not suitable for packaging and conveying angular heavy materials.